1. Field of the Invention
The invention relates to reinforced, especially, highly filled polyamide molding materials having improved processing behaviour, increased flowability, improved surface quality, and good thermal properties. The molding materials according to the present invention are suitable for production of molded articles, especially, having high wall thickness or other semi-finished products or finished articles, prepared for example, by extrusion, extrusion blow-molding, extrusion stretch-blow-molding, pultrusion, injection molding, gas assisted injection molding(GIT), injection-blow molding or other molding methods.
The molded articles produced by molding materials according to the present invention are used for production of interior and exterior parts, especially having supporting or mechanical function in the field of electricity, electronics, telecommunication, automobile, transport, packaging, domestic, furniture, sport, apparatus engineering, machine construction, heating installation, air conditioning, sanitary.
2. Background and Prior Art
Molded materials from reinforced polyamide blends are of increasing importance in the field of technical engineering materials which have to show besides high rigidity, tenacity and heat dimensional stability for uses in visual range also an optimal surface quality. Exterior parts being exposed to weathering require additionally an appropriate stability to ensure the necessary function for several years.
The special advantage of reinforced polyamides is the extremely good bond between polymer matrix and reinforcing materials. Thereby, high reinforcing ratios are possible leading to high-rigidity products having good processable in injection molding process due to the low melt viscosity of semi-crystalline polyamides.
In the following, polyamides have to be understood to be such polymers, wherein the monomer units are mainly, i. e. up to at least about 60%, linked together by amide bonds, i.e. by CO—NH-bonds and constituted of lactams, amino acids or diamines and dicarboxylic acids. Suitable monomers for production of polyamides are: caprolactam, laurolactam, aminocaproic acid, aminoundecanoic acid, aminododecanoic acid, diaminobutane, hexamethylenediamine, methylpentamethylenediamine, 3,3′-dimethyl-4,4′-diaminocyclohexylmethane (MACM), 1,6-diamino-2,2,4-trimethylhexane, 1,6-diamino-2,4,4-dimethylhexane, m-xylylenediamine, p-xylylenediamine, diaminononane, diaminodecane, diaminododecane, 2,2-bis(p-aminocyclohexyl)propane, bis(p-aminocyclohexyl)methane (PACM), isophorondiamine, polypropyleneglycoldiamine, diaminonorbornane, 1,3-bis(aminomethyl)cyclohexane, TCD diamine, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecandioic acid, dimer acid, terephthalic acid, isophthalic acid, cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, tert-butyl isophthalic acid, and phenylindanedicarboxylic acid. Also, the reaction of the acid chlorides or esters to polyamides is included as the polycondensation is the commonly used process.
The designation of the polyamides corresponds to international standard ISO 1874-1: the first number indicating the number of C atoms of the starting amine and the last number indicating the number of C atoms of the dicarboxylic acid. When only one number is given, that means that one starts from an amino-carboxylic acid or its lactam, respectively (see, H. Domininghaus, Die Kunststoffe und ihre Eigenschaften, published by VDI 1976, p. 272).
Thereby, the diamine is always cited at first position for AA-BB type polyamides. For example, the polyamide from hexamethylenediamine and sebacic acid is designated as polyamide 610 (PA 610), the polyamide from caprolactam is designated as PA 6.
Sometimes, special combinations of letters exists for aromatic and cycloaliphatic monomers, for example, T for terephthalic acid, I for isophthalic acid.
The components are separately listed by slash in order of their parts per amount and are followed by the parts per amount within brackets, e. g. copolyamide 6/66/610 (50:30:20) to characterize copolyamides.
The number average molecular weight of the polyamides described herein should be over 5000, preferably over 7000.
The drawback of reinforced semi-crystalline polyamide molding materials such as, for example PA 66, is the strong decrease of the rigidity by water absorption in standard operating environment. Reinforced polyamide molding materials (PA 66) tend to have poor surfaces, in particular, for molded parts having high wall thickness due to the high melt temperature and an extremely high velocity of crystallization.
Inclusion of high amounts of reinforcing materials such as, for example glass fibres, into a rapidly solidifying PA 66 polymer matrix reduces the flowability, for example, during the injection molding processing and leads to reduced surface quality. In these cases, one attempts to maintain the filling ratio low and to achieve the rigidity by reinforcing ribs.
From DE-A-17 69 040 (Dynamit Nobel AG) non-reinforced molding materials of semi-crystalline aliphatic polyamides and amorphous copolyamides being mixed in an extruder are known.
DE 26 42 244 C2 (Inventa AG) indicates that reinforced molding materials can be produced by extruding amorphous MACMI/12 type copolyamides and semi-crystalline aliphatic polyamides, thereby changing the mechanical properties.
EP 70001 B2 (Dupont) describes non-reinforced and reinforced molding materials on the basis of semi-crystalline aliphatic polyamides and amorphous polyamides consisting of 40-98 mol-% of units of isophthalic acid, 2-60 mol-% of units of terephthalic acid, 50-98 mol-% of units of hexamethylenediamine and 2-50 mol-% of units of bis(P-aminocyclohexyl)-methane (PACM). Thereby, the tenacity (tensile strength) of the molding materials should be improved. The drawback of these mixtures is the risk that inhomogenities in the molded article can arise as a result of phase separation.
By adding 30-95 wt.-% of amorphous polyamides such as, for example, hexamethylene isophthalamide PA 6I (DE 37 05 228 A1, EP 279 342 A1) (Bayer AG) to reinforced PA 66 improved flow properties in the melt and increased elongation at break in the molded part are found. At the same time an improvement of the surface quality (DE 32 00 428 C2) (Bayer AG) is found. The drawback of these mixtures is the risk that inhomogenities in the molded article can arise as a result of phase separation. Further, the heat dimensional stability decreases with increasing amount of PA 6 I . The difference of the rigidities in the dry and conditioned state increases with decreasing amount of PA 6 I.
EP 400 428 A1(BASF AG) describes molding materials of semi-crystalline semi-aromatic copolyamides (6T/6) extruded with amorphous copolyamides (6I/6T: 60/40 wt.-%). These molding materials show an improved tenacity with regard to pure CoPA 6T/6 and PA 66, but have, in comparison to CoPA 6T/6I , low melting points. A drawback of these products is the strong decrease of rigidity after water absorption. Additionally, these low melting points have a disadvantageous effect on the heat dimensional stability.
EP 0 728 812 A1(BASF AG) describes thermoplastic molding materials of a semi-crystalline semi-aromatic copolyamide including 30-44 mol-% of units of terephthalic acid, 6-20 mol-% of units of isophthalic acid, 43-49.5 mol-% of units of hexamethylenediamine and 0.5-7 mol-% units of an aliphatic alicyclic diamine and an amorphous polyamide. The drawback of these compositions is the decrease of properties such as HDT (Heat Deflection Temperature) with increasing amounts of an amorphous polyamide such as e. g. PA 6I/6T.
To obtain improved surface quality and good rigidity EP 0 532 963 A2 (BASF AG) proposes thermoplastic molding materials on the basis of polyamide blends of 1-18 wt.-% of a semi-crystalline semi-aromatic copolymer and 22-99 wt.-% of a semi-crystalline polyamide. The substitution of this semi-crystalline polyamide by an amorphous polyamide results to a reduction of gloss.
Excellent surface qualities at high filling ratios are obtained (DE 43 21 247 C2 (Asahi)), when a copolymer such as, for example a PA 66/6I, is produced from the constituents of a semi-crystalline polyamide such as PA 66 (70-95 wt.-%) and an amorphous polyamide such as PA 6I (5-30 wt.-%). The constancy of the mechanical properties in both dry and conditioned state is unsatisfactory. The decrease of the melting point has a undesirable effect on the heat dimensional stability, also indicated as HDT (Heat Deflection Temperature).
Improved flowabilities without negative effect on the tenacity, rigidity and heat dimensional stability can be obtained by addition of 4-8 wt.-% of a PA prepolymer based on the amount of the polymer matrix (DE 198 21 719 A1(EMS-Inventa AG)). A 6T/6I type semi-aromatic PA of the composition 70/30 wt.-% having relative viscosities of 1.01 to 1.3 as measured in 0.5% solution of m-cresol is used as PA prepolymer to a polymer matrix of PA 66, PA 66+PA 6I/6T (blend) or PA 12. The flow lengths and surfaces of the molded parts can be strongly improved despite of high filling ratios of 50-70% of glass fibres. Again, the drawback of these mixtures is the risk that inhomogenities in the molded article can arise as a result of phase separation. Further, blends, for example on basis of PA 66 with PA prepolymer, show still strong differences for the rigidity in dry and conditioned state. However, these blends described by DE 198 21 719 show a low HDT in comparison to a PA 6T/6I.
Still, an unpublished application DE . . . (EMS-Chemie AG) describes that the combination of a corresponding copolymer such as, for example, PA 66/6I/6T or of PA 6/6I/6T and amorphous PA 6I/6T and PA prepolymer such as, for example, PA 6T/6I having very low viscosity, improvements of the flowability and surface quality are possible, without the risk of inhomogenities in the molded article by phase separation of the blends. Simultaneously, by appropriate selection of the components HDT, tenacity and rigidity can be adjusted to an acceptable level and the influence of water absorption while conditioning can be reduced. However, altogether these blends show a relatively low HDT in comparison to a PA 6T/6I.
JP-A-7090178 (Mitsubishi) describes polyamide compositions which can be processed to molded parts, sheets, injection-molded or extruded parts. These polyamide compositions are supposed to have good mechanical properties such as high flexural strength not only at normal, but also at high temperatures. The polyamide compositions as described by JP-A-7090178 (Mitsubishi) should consist of 95 to 25 parts per mass of a crystalline, aromatic polyamide resin having a melting enthalpy of at least 3 cal/g, which consist of dicarboxylic acid units consisting of 30-100 mol-% of units of terephthalic acid and 0-40 mol-% of units of aromatic dicarboxylic acid other than units of terephthalic acid and/or 0-70 mol-% of units of aliphatic dicarboxylic acid and units of aromatic and/or alicyclic alkylenediamine and 5-75 parts per mass of a non-crystalline or low-crystalline polyamide resin having a melting enthalpy of not more than 1 cal/g and 5-200 parts per mass of inorganic fibres based on 100 parts per mass of polyamide resin. According to JP-A-7090178 by adding the crystalline aromatic polyamide resin instead of a crystalline aliphatic polyamide resin a positive effect on the flexural strength and flowability is achieved. However, HDT, tenacity, rigidity and the surface quality can not be increased simultaneously to a high level by the selection of the component according to JP-A-7090178. With higher amounts of the amorphous component the heat dimensional stability is decreased strongly. In addition, the mechanical thermal properties such as for example low creep at conditioned state can not be satisfied by the molding materials according to JP-A-7090178.
EP 1018534 A2 (Ube Industries) describes polyamide resin compositions having improved weld line strength. The polyamide compositions comprise 95-55 wt.-% of a crystalline semi-aromatic copolyamide having an aromatic monomer unit (6T) and a melting point of 260-320° C. and/or a crystalline aliphatic polyamide resin and 5-45 wt.-% of a polyamide resin comprising units derived from xylylenediamine and units of an aliphatic dicarboxylic acid or a non-crystalline semi-aromatic polyamide resin composition having at least 2 aromatic monomer units. Further, the polyamide composition according to EP 1018534 A2 comprises 5-200 parts per weight of an inorganic filler. There is disadvantageous that the PA-compositions as described have only glass transition temperatures up to 100° C. In particular, the melting points being partly very low have a negative effect on the heat dimensional stability. The constancy of properties in conditioned state is unsatisfactory.